Summary of Work: Tumor growth and viability can be monitored by measuring the rate of glucose metabolism in the tumor, using fluorodeoxyglucose (FDG) positron emission tomography (PET). The goal of this imaging physics project is to assess various quantitative measures of tumor FDG uptake for this purpose and, if possible, as indices of response to therapy. It was postulated that the usual method for measuring glucose uptake - the so-called "standardized uptake value" - would produce values that were too strongly influenced by the metabolic state of other body organs and by the time of imaging. instead, it was proposed to normalize the glucose uptake by the integral of the arterial deoxyglucose concentration curve. This curve is to be determined from a combination of cardiac bloodpool imaging (during the first 20 minutes post-injection), and intravenous blood sampling (during the remainder of the study). The study is to utilize subjects undergoing PET FDG imaging for evaluation of colon cancer. In addition, previously acquired data from subjects undergoing FDG imaging for liver cancer will be analyzed. We are also investigating the possibility of using some "control" data from subjects who have previously undergone FDG cardiac imaging. The first phase of the project involves estimating the errors associated with using intravenous samples for late estimates of the arterial curve. The second phase will compare uptake values at early and late times in tumors and normal tissue, using the proposed arterial curve normalization and the conventional scheme of normalization (lean body mass and injected activity).